"I'll go for a little more," Keys said Thursday night at the Apollo Theater, where her charity's annual gala was held.
The man - pharmaceutical billionaire Stewart Rahr - didn't raise his bid, but he later pledged $1 million to Keep a Child Alive, helping the R&B singer raise more than $2.9 million.
Keys' charity assists those affected by HIV/AIDS in Africa and India. Thursday's event was originally planned for Nov. 1, but was canceled due to Superstorm Sandy.
"There are places in the world where Keep a Child Alive serves where they have a Hurricane Sandy every day," Keys said in an interview on the red carpet. "They don't have electricity, they don't have heat ... and that made me more invigorated to make sure this Black Ball happened."
Keys honored Oprah Winfrey at the event for the entrepreneur's philanthropic efforts, including her school, The Oprah Winfrey Leadership Academy for Girls in South Africa, which launched in 2007.
"It's a universal truth, Oprah makes change happen," Keys said.
Winfrey said she was honored to receive an award from Keys, and that it confirms she's "moving in the right direction."
"You try to keep a child alive and I try to educate them as best as I can," Winfrey said onstage.
Before that, a video played onscreen detailing the launch of Winfrey's school and how the mogul struggled in her early years, riding on a bus with maids from the inner city to the suburbs to attend a better high school.
"When I look at Africans girls I see myself," 58-year-old Winfrey said. "I continue to work for them to have the same opportunities that I have. "
Beninese singer Angélique Kidjo was also honored and she joined Keys onstage for some upbeat, drum-filled numbers.
Bonnie Raitt also performed, as she and Keys sang a duet version of her slow groove "I Just Can't Make You Love Me." Keys said it was "one of my dreams to sing" with Raitt.
Jennifer Hudson and Brittany Howard of Alabama Shakes also hit the stage, where Whoopi Goldberg worked as the night's emcee.
"I read '50 Shades of Grey' so I stay away from paddles," Goldberg said when the auction began.